In a wireless communication system, wireless portable Internet is a next-generation communication system that supports mobility and local area data communication, such as in a conventional wireless local access network (LAN) that uses a fixed access point.
In such a wireless portable Internet system, a mobile access terminal (AT) requires a ranging to access an access point (AP). The ranging in a wireless portable Internet system is a function that controls transmission power, timing, and frequency offset of an uplink so that the AP can receive accurate data from the AT. When the AT periodically transmits Code Division Multiple Access (CDMA) codes to the AP, and the AP receives the CDMA codes, estimates transmission parameters (transmission power, timing, and frequency offset), controls the transmission parameters to be within a range set for receiving accurate data, and transmits the controlled transmission parameters to the AT.
In more detail, a ranging process is divided into an initial ranging and a controlling ranging. During the initial ranging, the AT selects a resource from among uplink resources provided by the AP and initially accesses the AP by transmitting a CDMA code assigned to the AT to the AP through the selected resource. During the controlling stage, the AT periodically performs receiving and processing a ranging response (RNG_RSP) message transmitted from the AP that has received the CDMA code and controlling transmission parameters of the uplink. In general, the controlling ranging is performed at predetermined intervals to periodically control transmission parameters so that the AP receives data from the mobile AT with accuracy even though a wireless data communication environment dynamically changes as the AP moves from one area to another.
However, a conventional ranging is performed at fixed intervals without considering changes of the wireless data communication environment, and thus it is difficult to control transmission parameters when the AT moves vary fast. Moreover, since the ranging is performed at fixed intervals when the AT is fixed, CDMA codes transmitted from different ATs may be collided with each other in a contention-based CDMA code transmission, thereby causing degradation of a wireless communication system.